LA-8437-MS bInformal Report -~*z... - f

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Numerical Modeling of

Insensitive High-Explosive Initiators

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UNITCO STATCSDEPARTMENT OF CNIZSt~V

CONTRACT W-740 B-CNG. 36

LA-8437-MS

Informal Report

UC-45Issued: July 1980

-.

Numerical Modeling of

Insensitive High-Explosive Initiators

Charles L. Mader

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NUMERICAL MODELING OF INSENSITIVE HIGH-EXPLOSIVE INITIATORS

by

Charles L. Mader

ABSTRACT

The initiation of propagating detonation in PBX-9404,PBX-9502, and x0219 by hemispherical initiators of PBX-9404,1.8 g/cm3TATB, and X0351 is described numerically, usingthe two-dimensional Lagrangian code 2DL and the Forest Firerate to describe the heterogeneous explosive shock initia-tion process.

1. INTRODUCTION

The initiation of propagating, diverging detonation is usually accomplishedby small conventional initiators; however, as the explosive to be initiated be–comes more shock insensitive, the initiators must have larger diameters (>2.5 cm)to be effective.

Travisl has used the I*C camera to examine the nature of the diverging det-onation waves formed in PBX-9404 (94/3/3 HMX/nitrocellulose/Tris-&chloroethylphosphate), X0290 or PBX-9502 (95/5 TATB/Kel-F at 1.894 g/cm3), and X0219 (90/10TATB/Kel F at 1.914 g/cm3) by hemispherical initiators. The geometries of theinitiators were (1) a 6.35–mm-radius hemisphere of PBX-9407 (94/6 RDX/Exon at1.61 g/cm3) surrounded by a 6.35-mm-thick hemisphere of PBX-9404, (2) a 6.35-mm-radius hemisphere of 1.7-g/cm3 TATB surrounded by a 19.05-mm-thick hemisphere of1.8-g/cm3 TATB, or (3) a 16-mm-radius hemisphere of X0351 (15/5/80 HMX/Kel-F/TATBat 1.89 g/cm3).

We have numerically examined systems with similar geometries by use of thehydrodymmic code 2DL2and the Forest Fire rate2 to describe the shock initiationprocess.

II. NUMERICAL MODELING

The two-dimensional reactive Lagrangian hydrodynamic code 2DL2 was used todescribe the reactive fluid dynamics. The Forest Fire2 description of hetero-geneous shock initiation was used to describe the explosive burn. The HOM equa-tion of state and Forest Fire rate constants for PBX-9502, PBX-9404, and X0219were identical to those described in Ref. 2. The Pop plots are shown in Fig. 1

1

and the Forest Fire rates in Fig. 2. The BKW detonation product equation-of-state constants for X0351 and for 1.7- and 1.8-g/cm 3 TATB are given in Tables I,II, and III.

The calculations were done in cylindrical geometry with Lucite confinementrather than the air confinement present in the experimental study. The Lucite

confinement prevents the mesh distortion that can be fatal to Lagrangian calcula-tions.

The central 6.35-mm region of the detonator is initially exploded, whichinitiates the remaining explosive in the detonator using a C-J volume burn. For

any given mesh size and time step, the viscosity must be adjusted to give a peakpressure at the detonation front near the effective C-J pressure. The parameters

used are as follows.

Calculation Mesh Size Time Step ViscosityInitiator Acceptor (cm) (lls) Coefficient

PBx-9407/PBx-9404 PBX-9404 0.05 0.02 4.0PBx-9407/PBx-9404 PBX-9502 0.05 0.02 5.0PBx-9407/PBx-9404 X0219 0.05 0.02 4.21.7 TATB/1.8 TATB PBX-9502 0.1 0.02 5.0X0351 PBX-9502 0.1 0.02 5.0

The pressure and mass fraction contours are shown for a PBX-9404 hemisphereinitiating PBX–9404 in Fig. 3, PBX-9502 (X0290) in Fig. 4, and x0219 in Fig. 5.The experimental and calculated position of the leading wave as a function ofdistance from the origin is shown in Fig. 6.

The burn can become unstable when it turns a corner. The instability isapparently numerical because it can be eliminated by using an average of nearbycell pressures for the Forest Fire burn rather than the individual cell pressure.

The pressure and mass fraction contours are shown in Fig. 7 for the 1.8-g/cm3 TATB hemisphere initiating PBX-9502. Veqr little undecomposed explosive wasobserved experimentally, in agreement with the calculated results. The contoursare shown in Fig. 8 for an X0351 hemisphere initiating PBX-9502. The experimen-tal and calculated regions of partially decomposed PBX-9502 are shown in Fig. 9.

III. CONCLUSIONS

The initiation of propagating detonation in sensitive (PBX-9404) and insen-sitive (PBX-9502 and X0219) explosives by hemispherical initiators can be de–scribed numerically using the two-dimensional Lagrangian code 2DL and the ForestFire rate. Large regions of partially decomposed explosive occur even when in-sensitive explosives are initiated by large initiators.

REFERENCES

1. James R. Travis, Los Alamos Scientific Laboratory, personal communication.

2. Charles L. Mader, Numerical Modeling of Detonations (University of CaliforniaPress, Berkeley, 1979).

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